Theo Grant and Harper Lily Ellis-Grant had been married eight years when their family felt complete.

At thirty-four, Harper was a veteran leader with the Boston Fleet—captain, three championships, a voice in the league for player safety and mental health. Theo, thirty-six, was head of sports orthopedics at a major hospital—steady in the OR, calm under pressure, the dad who could fix a broken toy and a broken heart with the same gentle hands.

Their children were the center ...